Recently, human infection of avian influenza (bird flu) has been reported, and there is a concern about heavy damage caused by widespread human-to-human transmission of bird flu (pandemic). Because of this situation, pre-pandemic vaccine, which is possibly effective against bird flu, is being stockpiled worldwide. Further, to administer the pre-pandemic vaccine to many people, studies are being carried out on increasing the production of vaccine.
Skin is composed of three parts: epidermis, dermis and subcutaneous tissue. The epidermis is a layer of about 50-200 μm from the skin surface, and the dermis is a layer of about 1.5-3.5 mm continuing from the epidermis. Since influenza vaccine is generally subcutaneously or intramuscularly administered, it is administered to the lower layer of skin or a portion deeper than that.
On the other hand, it has been reported that by administering influenza vaccine to the upper layer of skin as a target site where many immunocompetent cells are present, the same immunity acquisition ability as in subcutaneous administration or intramuscular administration can be obtained even with a reduced dosage (Non-patent Document 1). Thus, by administering bird flu vaccine to the upper layer of skin, the dosage can be reduced, so that there is a possibility that bird flu vaccine can be administered to more people. Incidentally, the upper layer of skin refers to the epidermis and dermis of skin.
As the means of administering a drug to the upper layer of skin, methods have been reported such as using a single-needle, a multi-needle, a patch, gas and the like. Considering the stability and reliability of administration and production cost, the method of using a single needle is the most suitable means of administering a drug to the upper layer of skin. As the method of administering vaccine to the upper layer of skin using a single needle, the Mantoux method has been known for a long time. In the Mantoux method, a needle of generally 26-27 G in size having a short bevel needle tip is inserted into the skin about 2-5 mm, from an oblique direction of about 10-15° relative to the skin, to administer a drug of about 100 μL.
However, the Mantoux method is difficult to manipulate and is affected by the skill of the doctor who gives the injection. In particular, it is difficult to administer flu vaccine to a child with the Mantoux method because the child may move during the administration. Accordingly, it is desired to develop a device that can administer vaccine to the upper layer of skin in a simple and convenient manner.
Patent Document 1 describes an injection device for administering a drug to the upper layer of skin. In the injection device, a limiter having a skin contacting surface is connected to a needle hub. The limiter of the injection device described in Patent Document 1 is formed in a tubular shape covering the circumference of a needle tube, and has a gap with the needle tube. By defining the length (protruding length) of the needle tube protruding from the surface of the limiter contacting the skin as a range of 0.5-3.0 mm, the drug is administered in the skin.
Further, Patent Document 2 describes a puncturing adjustment tool for injection needle adapted to prevent the injection needle from puncturing the skin deeper than a target depth. The puncturing adjustment tool for injection needle described in Patent Document 2 includes the one formed in a tubular shape covered around a injection needle, and has a gap with the injection needle. Further, the tubular puncturing adjustment tool for injection needle described includes the one in which the needle tip of the injection needle is formed in a position not protruding from the end portion. When strongly pressing such a puncturing adjustment tool for injection needle against the skin, the skin inside the puncturing adjustment tool for injection needle is raised, and thereby the injection needle is inserted into the skin. Further, the puncturing adjustment tool for injection needle disclosed in Patent Document 2 includes the one which closely contacts the circumference of a needle tube.    Patent Document 1: Japanese Laid-open Patent Application Publication No. 2001-137343    Patent Document 2: Japanese Laid-open Patent Application Publication No. 2000-037456    Non-patent Document 1: R. T. Kenney et al. New England Journal of Medicine, 351, 2295-2301 (2004)